1. Field of the Invention
The present invention relates to fiber optical apparatus, and particularly to tools that indicate the direction of a light signal in an optical fiber.
2. Discussion of the Known Art
So-called live optical fiber identifier tools are generally known. See, e.g., U.S. Pat. No. 5,708,499 (Jan. 13, 1998), and U.S. Pat. No. 5,138,690 (Aug. 11, 1992); and U.S. Pat. Appl'n Pub. No. 2008/0192241 (Aug. 14, 2008), all of which are incorporated by reference. FIGS. 1 and 2 of the present application are side and front views of an optical fiber identifier tool 1 currently available from OFS Fitel, LLC, Norcross, Ga. 30071 USA, as model No. ID-H/R.
The tool 1 detects and indicates the direction a light signal is traveling in an optical fiber, whether the fiber is contained in a cable or is one among a number of ribboned fibers, without having to disconnect the fiber or otherwise disrupt signal traffic in an associated network. A length of the fiber is aligned in a slot or groove 2 formed in a head portion 3 of the tool 1. A trigger 4 on the tool 1 is fastened by a screw to an internal clamp mechanism, and the mechanism causes the fiber to bend a certain amount inside the head portion 3 when the trigger 4 is pulled downward along the side of the tool body. As is generally known, a small fraction of a light signal traveling in the fiber will leak out from the region of the fiber bend. The tool 1 also has a control panel 5 including a power on/off switch 6, live signal direction indicator lamps 7, and a tool status and measurement data display screen 8.
Two photo detectors are mounted at determined positions inside the head portion 3 of the tool 1. The photo detectors are disposed so that depending on the direction the light signal is traveling in the fiber, a greater amount of the light that leaks from the fiber bend is incident on one of the detectors than on the other detector. Live fiber identifier tools are generally quite effective and often used in fiber optic data centers, FTTx, and related applications.
It is not uncommon for a live fiber identifier tool to produce false indications when used in direct sunlight and even in shaded areas outdoors, however. Even when no signal is present in a fiber under test, ambient light can leak inside the head portion of the tool near the photo detectors and cause either one or both of the detectors to respond, thus making the tool falsely indicate that signal traffic is present. To help avoid this problem, a rubber light shield is available from Fujikura Ltd, Japan, as an accessory (No. LSR-02) for the company's model FID-25R/26R optical fiber identifiers.
The known light shield is made to be placed by hand over the head portion of the tool when testing a fiber. Once placed over the tool, the operator must use one hand to keep the shield in place and, at the same time, use the other hand to operate the tool to take a measurement. Therefore, by the time the measurement is taken, the shield is likely to have shifted from a most effective position so as to allow enough ambient light to enter the tool to cause a malfunction. Accordingly, there remains a need for a light cover or hood for a fiber identifier tool that is convenient to use, and which will operate reliably to block outside light under all conditions.